1. Field of the Invention
The present invention relates to a tape carrier and a manufacturing method thereof. More particularly, the present invention relates to a tape carrier, on the tape base material of which a plurality of metallic wires are formed through an adhesive layer, and in the tape base material of which a plurality of via holes communicated with the metallic wires are formed. Also, the present invention relates to a method of manufacturing the tape carrier.
2. Description of the Related Art
Recently, semiconductor elements such as IC chips are highly integrated and mounted on electronic devices at high density. In accordance with that, various semiconductor devices (tape carrier packages), in which tape carriers are used, have been developed and put into practical use. Concerning the material used for the tape carrier (TCP), three layer tapes are commonly used, on which a layer of copper foil is made to adhere onto an insulating tape base material made of polyimide through an adhesive layer.
Description will be given to a common manufacturing method of BGA (Ball Grid Array) type tape carrier in which the above three layer tape is used. First, in a tape material in which an adhesive layer is formed on a base material made of polyimide, punching to form various openings is conducted so that device holes, outer lead holes, via holes and sprocket holes are formed.
Next, a layer of copper foil is laminated on the side of the tape material, which has been punched and on which the adhesive layer is formed, so that a three layer tape can be formed. The above copper foil is subjected to photolithography of the prior art, and a wiring pattern is formed using the copper foil. The above wiring pattern is subjected to tin plating, solder plating, nickel plating or gold plating. Then, solder balls are put on the via pads exposed to the via holes and reflowed so that the solder bumps are formed. In this way, the tape carrier is manufactured.
In the above method of manufacturing the tape carrier, the tape material is punched. Examples of the punching method are: a punching method conducted by a press, a method of forming holes by means of laser beams, and a method of forming holes by means of etching.
From the viewpoint that the number of manufacturing processes is small and the production cost is low, the punching method conducted by a press is preferably used. In the case of punching a tape material, on the polyimide base material of which the adhesive layer is formed, when punching is conducted from the polyimide base material side, a burr of the adhesive layer is generated. Therefore, punching is commonly conducted from the adhesive layer side to the polyimide base material side.
However, when the tape material 51 is punched from the adhesive layer 52 side in the direction of arrow E, sags are caused on the adhesive layer 52 at the opening edge portion as shown in FIG. 9. Therefore, the adhesive enters the via hole 53. When the layer of copper foil 54 is laminated on the adhesive layer 52 under the condition that the sags are generated on the adhesive layer 52, there is caused a gap 55 between the copper foil 54 and the adhesive layer 52 by the influence of the sags. When the metallic wire 57 including the via pad 56 exposed to the via hole 53 is formed by etching the layer of copper foil 54 as shown in FIG. 10, an adhesive area of the via pad 56 is reduced by the sags of the adhesive layer 52. Accordingly, there is a possibility that the via pad 56 can be peeled off and that the reliability of the package can be deteriorated.
Therefore, for example, when the diameter of the via hole is .phi.0.200 mm and consideration is given to the sags of the adhesive layer 52, adhesive region R of the via pad 56 with respect to the tape material 51 must be at least 50 .mu.m on one side in the radial direction. More preferably, adhesive region R of the via pad 56 with respect to the tape material 51 must be approximately 75 .mu.m on one side in the radial direction. Unless the above adhesive region R is ensured, it is impossible to maintain the reliability of the package.
As described above, the diameter of the via pad to be joined to the solder ball 58 must be larger than a predetermined value. When the wiring pattern, the wiring pitch of which is made to be fine, is designed, this extended via pad diameter puts a great restriction on the design of the wiring pattern.
In order to join the solder ball 58 to the via pad 56 exposed to the via hole 53 as shown in FIG. 10, when consideration is given to the wettability of the solder and the pad surface, it is necessary that the solder ball 58 comes into contact with the via pad 56. The size of the solder ball 58 is restricted by the via hole diameter, the tape material thickness and the solder ball diameter. In this case, there are two requirements which are incompatible with each other. One requirement is that the via hole diameter tends to be decreased when the pitch of the wiring pattern is made to be fine. The other requirement is that the solder ball diameter is made as large as possible for increasing the height of the solder bump as high as possible when the base board or IC chip 59 is mounted on the solder bump.
In the conventional tape carrier, for example, when the solder ball 58, the diameter of which is not less than .phi.0.200 mm, is inserted and jointed to the via hole 53, the diameter of which is .phi.0.200 mm, there is a possibility that the solder ball 58 can not be sufficiently joined to the via hole 53. Actually, it is impossible to join the solder ball 58 to the via hole 53. When the thickness of the tape material 51 is decreased to as small as possible, the following problems may be encountered. In general, the tape material 51 is in a belt-shape and moves between the reels. While a predetermined tension is given to the tape, it is conveyed. Therefore, when the mechanical strength of the tape material is lowered, it becomes difficult to convey the tape. For the above reasons, thickness of the tape material 51 can be reduced only to 50 .mu.m.